1. Field of the Invention
The present invention relates to a battery capacity measuring system, and more particularly to a battery capacity measuring system which removes a singular point of data by demarcating a range of data to be employed on the basis of the data representative of the battery capacity at the previous running.
2. Description of the Related Art
In a prior battery capacity measuring system, the measurement of the battery capacity depends upon the obtained coefficient of correlation between a plurality of voltage values and a plurality of current values corresponding thereto, and when this correlation coefficient assumes a large negative correlation (for example, below -0.9), an approximate straight line is attained by processing these voltage values and current values through the use of the method of least squares.
In addition, the voltage at the intersection (node) between the approximate straight line and a predetermined reference (criterion) value is converted into a remaining capacity and put to display.
However, in cases where such a battery capacity measuring system is incorporated into an electric motor vehicle or the like, the electric motor vehicle generates a lot of noise, with the result that, when collecting a plurality of voltage values and a plurality of current values, as shown in FIG. 5 some data can reside at a place(s) (which will be referred to hereinafter as a singular point) abnormally remote from places where many data gather.
If obtaining an approximate straight line on the basis of the coefficient of correlation (for example, -0.96) irrespective of the presence of such a singular point, the resultant approximate straight line lies as indicated by a dotted line b in FIG. 6. On the other hand, when attaining an approximate straight line as function of the coefficient of correlation (for instance, -0.99) in the absence of the singular point, the resultant approximate straight line is indicated by a solid line a in FIG. 6.
More specifically, as shown in FIG. 6 the inclination of the approximate straight line varies in accordance with whether the singular point exists or not. This signifies that the obtained approximate straight line involves an error in the presence of the singular point.
The prior battery capacity measuring system is designed to calculate the approximate straight line if the coefficient of correlation between pluralities of voltage values and current values collected merely comes to below -0.9, and therefore, in many cases the resultant approximate straight line involves the singular point.
One possible solution of the problem in the approximate straight line involving singular points may be that the coefficient of correlation serving as the decision condition is set to approximately -0.99. However, since the past data is additionally adopted for the approximate straight line, the coefficient of correlation can assume approximately -0.99 even if including the singular point, with the result that an error arises in the course of repeatedly attaining the approximate straight lines.